Hit hard by plunging oil prices and international sanctions, the Russian ruble slid Thursday to new lows of just over 46 to the dollar and 58 to the euro — part of its biggest weekly plunge since 2009.

The dollar rose to 46.77 rubles from 44.95, while the euro reached 58.11 rubles.

The ruble has lost about a quarter of its value so far this year, despite several interventions on the currency market by the Russian Central Bank. Some analysts, saying the ruble is still overvalued, are predicting a further decline of 10 percent into next year.

The ruble's decline coincides with a drop in the price of oil, Russia's main export. Prices are hovering at four-year lows of about $82 a barrel.

Russia's Interfax news agency said ruble's decline was also attributable to new reports of fighting in southeastern Ukraine.

The United States and the European Union have targeted key sectors of the Russian economy with sanctions as part of a push to punish Moscow for its support of pro-Russian separatists battling the Kyiv government for autonomy near the Russian border.